A cathode ray tube (“CRT”), one of typical display devices, has been extensively used in television sets or computer monitors, but fails to catch up with the recent trend of miniaturization and lightweight of electronic equipments, due to the heavyweight nature and inherent bulkiness thereof.
Thus, a variety of technologies have been developed in an effort to replace the cathode ray tube with new display devices, examples of which include a liquid crystal display (“LCD”) using an electric field optical effect, a plasma display panel (“PDP”) using a plasma discharge and an electroluminescence display (“ELD”) using an electric field light-emitting effect.
Among these devices, the liquid crystal display, which features thin lightweight configuration and low electricity operability, is showing rapid expansion in its range of applications with the improvement of liquid crystal materials and the development of fine pixel processing techniques, and is widely used in household television sets, desktop computer monitors, notebook computer monitors, large-sized flat panel television sets and so forth.
Most of the liquid crystal displays require the use of a separate backlight unit that serves as a light-flatting element for regulating the quantity of an incoming light to display images.
As shown in FIG. 1, a liquid crystal display module 1 for use in typical liquid crystal displays is comprised of a liquid crystal display panel 2 filled with liquid crystal, polarizing plates 4a and 4b for polarizing a light directed to the upper and lower surfaces of the liquid crystal display panel 2, a backlight unit 6 for supplying an uniform light to the liquid crystal display panel 2, a main support 8a for maintaining an external configuration of the liquid crystal display module 1, and a top case 8b. 
Unlike the cathode ray tube or the plasma display panel, the liquid crystal display panel 2 does not emit any light by itself but merely changes orientation or arrangement of the liquid crystal. This makes it necessary to provide, at the rear of the liquid crystal display panel 2, the backlight unit 6 for evenly surface-irradiating the light on an information display surface.
In this regard, the backlight unit 6 is classified into an edge type and a direct type depending on the position of a light source. As illustrated in FIG. 2A, the edge type backlight unit includes a light source 12 disposed at one edge of a light guide plate 14 for surface-irradiating a light. In contrast, the direct type backlight unit is subdivided into a dot type wherein a plurality of dot-like light sources 16a are mounted on a substrate 30 as shown in FIG. 2B and a line type wherein a plurality of linear light sources 16b are mounted on a substrate 30 as shown in FIG. 2C. In such direct type backlight units, the light sources are substantially evenly distributed on the entire surface of the substrate.
Examples of the light source conventionally used include an electroluminescence (“EL”) element, a cold cathode fluorescent lamp (“CCFL”) and a hot cathode fluorescent lamp (“HCFL”). In recent years, extensive use is made of a light emitting diode (“LED”) that has a broad area of color reproduction and is environmentally friendly.
Research has been made to develop methods of using the light emitting diode as a light source in the backlight unit. Subjects of the research include a method of taking advantage of a blue color light emitting diode and an yttrium aluminum garnet (“YAG”) fluorescent body, a method of using an ultraviolet emitting diode in combination with fluorescent bodies of red, green and blue colors, and a method of employing red, green and blue light emitting diodes to admix the lights generated from them.
The method of taking advantage of a blue color light emitting diode and an yttrium aluminum garnet (“YAG”) fluorescent body is disadvantageous in that the light source thus produced has a reduced ability to express the red color and a low light emitting efficiency. Likewise, the method of using an ultraviolet emitting diode in combination with fluorescent bodies of red, green and blue colors poses a drawback in that it is difficult to develop the fluorescent bodies, with the resultant light source exhibiting a deteriorated thermal characteristic.
The method of employing red, green and blue light emitting diodes is effective in designing the light source to have a broadened range of color reproduction, thank to the increased intensity of red, green and blue lights emitted from the respective light emitting diodes. However, the method has a problem in that it is difficult to compose a combination of diodes for a white surface light source.
In the meantime, along with the recent trend of pursuing a large-sized and high image quality display device, a demand has existed for a liquid crystal display capable of driving a screen by a local dimming method and a field sequential method. Further, in order to assure an improved color reproduction characteristic, attention is being paid on a method wherein light emitting diodes of red, green and blue colors are used independently and a white color light is obtained by mixing the lights of the respective light emitting diodes.
Moreover, with a view to meet the requirements of high luminance and increased color temperature, there have been developed lenses for collecting the lights emitted from light emitting diodes, semiconductor chips and diode materials.
In particular, a molding technique has been developed that includes the steps of mounting light emitting diodes on the top surface of a substrate having thin film patterns, forming a molded portion on the light emitting diodes through the use of epoxy, acryl or silicon resin, and placing a lens on the surface of the molded portion to increase the luminance. In recent years, development is focused on a high flux lens in which a lens is integrally formed with a molded portion.
Taking an example, U.S. Patent Publication No. 2002/0190262 discloses a light emitting device including a resin portion with an opening, a first semiconductor light emitting element and a semiconductor device disposed inside the opening of the resin portion, and a silicon resin provided in the opening to cover the first semiconductor light emitting element and the semiconductor device, wherein the opening has a shape close to an ellipse or a circle, thus forming a lens.
However, such a lens lacks an ability to compensate the difference in luminous flux that varies with the positions of red, green and blue light emitting diodes mounted on a printed circuit board, which makes it impossible to obtain a homogeneous white light. An increasing number of light emitting diodes should be employed as a liquid crystal display grows in its size, in which case it becomes even more difficult to mix the lights into a homogeneous white light.
As a solution to this problem, it has been conventionally proposed to collect the lights emitted from the respective light emitting diodes or to diffuse the lights in the form of side light emission. However, these solutions also fail to obtain a homogeneous white light due to the lack of consideration of the difference in characteristic depending on the positions of the respective light emitting diodes.
Further, in order for a backlight unit to employ, e.g., a local dimming technique that will be put in use in the future to make a selected part of a liquid crystal display screen visible to a user, it must be possible to selectively turn on or off a desired partial region of the total irradiation area. However, the conventional lens method and the light collecting method have a technical limit in conducting the task of turning on or off the partial region of a screen.